I Can See Clearly Now, the Cataracts are Gone: History of Treatment

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MECHANISM OF DISEASE

Operative techniques on the eye have certainly taken great leaps since they were first described. From using a simple needle to now using lasers and lens replacement. One of the most popular first methods described before the 18th century was called couching, where the cataract is not removed but rather pushed to the side so it can’t block light anymore. Although their vision relatively improved, patients often suffered from postoperative complications due to infection1

However, the indian surgeon Sushruta actually described another procedure, long ahead of his time. Extracapsular extraction involves the lens capsule being left intact and the cataract being removed. This was first performed in the mid 18th century in Paris. The cornea was cut into and the cataract was scraped from the lens cortex. Extraction in this method was slightly more efficacious than couching, but it still proved to have postoperative healing issues and chance of further opacification1

The first intraocular lens extraction was performed shortly after, but did not become popular until the mid 19th century almost 100 years later2. This involved removing the lens capsule to extract the cataract. This involved breaking the zonular fibers that held the lens in place. A variety of methods were employed to do this ranging from forceps, enzymatically, and to cryoextraction where the lens adheres to a frozen probe. However, the lens capsule has an important job in preventing the vitreous humor from making its way into the anterior segment of the eye. This proved to have severe complications such as retinal detachment and macular edema. The larger incision needed to extract the whole capsule has a slower healing process and greater risk of astigmatism1

As greater sterile technique was developed, extracapsular cataract extraction came back into favor in the 1970’s in the United States. The invention of the intraocular lens replaced the cataractous lens and improved vision even further. Without the lens, postoperative patients needed strong glasses to be able to refract light. IOLs provided for an alternative refractive method to improve quality of life. Ophthalmic viscosurgical devices also helped to keep the eye structures in place to prevent collapsing during surgery and maintain space1

Phacoemulsification came about in the late 1960s, although initially not met with much support3. The lens nucleus is aspirated through a smaller incision than extracapsular extraction. This advanced procedure results in a shorter recovery time and a more stable structure throughout surgery. Now, ophthalmic viscosurgical devices are used in further stabilizing the chamber during surgery and laser is also used to break the lens capsule and make the incision1

Even with all of these advances, cataract surgery can not produce perfect vision and still leads to postoperative infection, increasingly the older the patients are. 

As most diseases are able to be pharmacologically treated, there is a great interest in the development of drug treatment for cataracts with the possibility of being more cost-effective. As α-crystallins control the aggregation of the lens proteins, they serve as a clear target from drug therapy. Makley et al found that pharmacological chaperones aided in reversing αA-crystallin and αB-crystallin aggregation4. These molecules bind and stabilize proteins much like α-crystallin does. The most effective class of compounds for this job was found to be sterols, with the author screening and finding the most efficacious one in preventing aggregation. Lens transparency and protein solubility was seen in mouse models in vivo and human lenses ex vivo.   

As I stated earlier, antioxidants can be a reducer of oxidative stress, so oral and topical routes of application have been employed. For example, the flavonoid based compounds in Figure 1 were administered in varying degrees with some preventive success5

Figure 1. Different flavonoid compounds administered with different applications with varying success in preventing cataracts5.

The next important steps in drug delivery, like in many other fields, is nanotechnology. The inability of drugs to penetrate past the cornea proves to be a particular place of improvement. Nanoencapsulated anti-cataract molecules such as chitosan, polystyrene, hyaluronic acid have been shown to increase the ocular concentration of drugs5.

References

  1. Davis 2016
  2. Hubbel 1904
  3. Kelman 1967
  4. Makley 2015
  5. Sunkireddy 2015

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